1. Field of the Invention
The present invention relates generally to information handling systems and, more particularly, to minimizing dynamic crosstalk-induced jitter timing skew in the information handling system.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users are information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes, thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems, e.g., computer, personal computer workstation, portable computer, computer server, print server, network router, network hub, network switch, storage area network disk array, RAID disk system and telecommunications switch.
In the design of the information handling systems, data integrity at higher and higher clock rates is become more difficult to maintain because of crosstalk and other noise induced interference on the data signals of interest. Timing skew (TS), the uncertainty in the arrival of a signal edge, are typically influenced by the effects of crosstalk, simultaneous switching noise (SSN), data and clock jitter, and electromagnetic interference (EMI) among others. Crosstalk effects have a significant impact on the timing of digital circuits. This impact increases dramatically as designers migrate to smaller process technologies and faster clock frequencies. Crosstalk is localized electromagnetic interference (EMI), via capacitive and inductive coupling mechanisms, from one circuit that affects the signals in an adjacent circuit.
Generally, crosstalk coupling increases with increasing parallelism of signal conductors and clock/data edge rise rate. With the present transition to and adoption of the latest very high speed serial technology (e.g., PCI Express—“PCI-E,” Serial Attached SCSI—“SAS,” and fully buffered dual inline memory module (DIMM)—“FBD”) to computer bus design, crosstalk-induced timing skew is becoming more challenging to quantity and minimize in the presence of other noise sources inherent in the information handling system.
The EWG (Electrical Working Group) for PCI-E GEN1 and GEN2, has recognized the contributions to the jitter budget in their recent investigation of the REFCLK and have made appropriate changes to the timing budget by taking away 30 picoseconds from the initial timing budget. As clock frequencies are increased and circuit densities decreased, crosstalk contribution to jitter can only become more pervasive.
No formalized analytical and/or empirical methodologies have been developed to address this crucial and recurrent limitation of appropriately identify and characterizing crosstalk-induced jitter timing skew, on-the-fly, as a crucial component that contributes significantly to the timing skew budget.
Referring to FIG. 1, a static-crosstalk approach may be used to compute far-end (FEXT) and near-end (NEXT) crosstalk noise based upon weak-coupling theory. This theory assumes that the coupling from the victim signal to the aggressor signal is insignificant. As such, to compute crosstalk, the victim (VICTIM-Q for Quiet Victim) signal is kept at either low or high states and the aggressor signals are excited. The amount of noise measured at the Far and Near ends of the victim circuit are the crosstalk noise contributions from the aggressors. This is the “static” approach to quantify crosstalk noise.
The problem with the “static” approach is that in a realistic situation, just as the aggressors inject noise onto the victim bus lines, so can the victim inject noise onto the aggressor bus lines. The real amount of noise seen on each bus line is the sum of the aggressors and “victim” (VICTIM-A for Aggressor victim). A realistic approach that addresses coupling from the VICTIM-A is called the strong-coupling (or dynamic) crosstalk method (see FIG. 2). Limitation in the use of the weak-coupling approach is very apparent for high speed signals with rise times in the sub 50 picoseconds range. It gives rise to unaccounted jitter timing skew due to the limitations inherent with the static approach.